The
horse has a large muscular system which allows movement of the horse,
gives it definitions as well as allowing posture like standing by
contracting both muscle groups at the same time.

Click on photo to
enlarge

Click on photo to enlarge

There are three types of muscle

Voluntary
(striped) - which is found in the leg, neck, quarters etc. The horse has
complete control over these.

Involuntary
(smooth) - which is found in the alimentary canal, the walls of the arteries
etc. The horse has no conscious control over these muscles.

Cardiac
- which is found in the heart and contracts rhythmically.

When considering the anatomy of a riding horse it is the voluntary muscles
which are significant. These are divided in to two groups - Flexor muscles which
bend the joint and extensor muscles which straighten the joint. When a horse is
standing both muscles act simultaneously to stabilise the joint, thus preventing
either flexion or extension.